1. Field of the Invention
The present invention relates to a transmission assembly for a power unit of a vehicle. More particularly, the present invention relates to a transmission assembly having a shift drum operable to select one of a reverse gear and a plurality of forward gears, the shift drum having a reverse cam groove formed thereon, and a reverse stopper arm urged by an urging member into the reverse cam groove, the reverse stopper arm requiring an external force overcoming the urging force of the urging member in order engage the reverse gear, and not requiring an external force in order to disengage the reverse gear.
2. Description of the Background Art
A transmission assembly for a power unit a vehicle, for example, such as disclosed in the Japanese Patent Publication Laid-open No. 2001-74139 is well known.
According a transmission assembly, as disclosed in the Japanese Patent Publication Laid-open No. 2001-74139, when a shift drum in a neutral position is rotated for establishing a reverse gear, an external force, resisting an urging force of a spring member, acts on the reverse stopper arm. The reverse stopper arm, therefore, detaches from the reverse cam groove and comes into contact with the outer periphery of the shift drum at both ends of the reverse cam groove.
The transmission assembly, as disclosed in the Japanese Patent Publication Laid-open No. 2001-74139, is large because the diameter of the shift drum has to be made large in order to increase the number of speed change positions set at the shift drum.
A disclosure of a transmission assembly (Japanese Patent Application No. 2007-083263), has already been submitted by applicant, in which common speed change positions establishing either a reverse gear or a fastest forward gear is set at the shift drum in order to prevent the shift drum from becoming large even if the number of speed change positions set at the shift drum increases.
When the transmission assembly, as disclosed in the Japanese Patent Publication Laid-open No. 2001-74139, is applied for preventing a shift drum from becoming large in diameter by establishing a common speed change position for either the reverse gear or the fastest forward gear, it is necessary to apply an external force acting on the reverse stopper arm in a direction opposite to that of the urging force to the reverse stopper arm, even when the shift drum is rotated, in order to establish a fastest forward gear.
The present invention has been made to overcome such drawbacks. Accordingly, it is one of the objects of the present invention to provide a transmission assembly where a common speed change position for establishing either a reverse gear or a fastest forward gear is set on a shift drum in order to prevent the diameter of the shift drum from becoming large, without reducing operativity of the transmission assembly.